1. Field
The present invention relates to a power factor correction (PFC) device in three-phase power supply (hereinafter referred to as a three-phase PFC device) and a method for controlling the same, and more particularly to a PFC control method based on a delay of an input current signal of a three-phase inverter.
2. Description of the Related Art
Generally, an inverter is a power-supply converter (also called a power converter) for converting a DC voltage into a three-phase AC voltage (U, V, W). Due to high energy efficiency and convenience of output control, the inverter has been generally used to control motors for use in a variety of electronic products (e.g., washing machines, refrigerators, air-conditioners, microwave ovens, and elevators).
A rectifying circuit for rectifying a commercial AC power into a DC voltage and smoothing this rectified DC voltage is connected to the above-mentioned inverter, such that the DC voltage smoothened to a predetermined level is provided to the inverter. A power factor of this rectifying circuit is very low, i.e., about 0.5-0.6. Due to a phase difference between an input voltage (i.e., a voltage of AC power) and an input current (i.e., a current of AC power), a power factor is decreased, such that there arises a loss of power consumption caused by a reactive power.
In order to solve the above-mentioned problems, a conventional art carries out power factor correction (PFC) operations, which corrects a power factor to prevent the occurrence of a phase difference between an input voltage and an input current, using a switching control scheme. This switching control scheme detects a zero-crossing point of an input voltage, turns on a switching element at the detected point, turns off the switching element after the lapse of a predetermined period of time, and maintains an OFF status of the switching element until reaching a zero-crossing point of the next input voltage.
However, if a current signal increases in a three-phase inverter which uses a three-phase power supply to power on electronic products of large amounts of power consumption, a phase current is slower than a phase voltage, such that there is a disadvantage in the above-mentioned conventional PFC control method allowing the switching to be carried out at a zero-crossing point of the phase voltage for power factor correction. In other words, according to the conventional PFC control method, a product having a high-current power environment and a high-capacity inverter is unable to begin performing the PFC switching at a desired point as the used current increases, and a phase difference between the voltage and current signals increases by any PFC switching errors caused by the delayed current, such that the power factor decreases even more, resulting in the increase in power consumption.